Telephone plug



Mardi 17, 1959 R. G. BARKER 2,878,459

TELEPHONE PLUG Filed May 5, 1958 /5 'E f Ilwllllllllrlllge'll fifiINVENTOR.

RAN DOLFH G. BARKER MVA-@MW ATTORN EYS 2,878,459 Patented Mar. 17, 1959TELEPHUNE PLUG Randolph G. Barker, West Bridgewater, Mass. v ApplicationMay 5, 1958, Serial No. 732,965

1 Claim. (Cl. 339-183) This invention relates to an improvedl telephoneplug for use with a standard switchboard. A telephone plug must becapable of engaging in a standard jack inv a switchboard. Plugs `forsuch use have two terminals consisting respectively of a ball tipand atube about an inch long, both terminals having a diameter of one quarterinch. These terminals are connected respectively to the wires of acoaxial cable, the ball. tip being connected to the inner wire, the tubebeing connected to the outer wire which is insulated from the inner wirebutv is arranged to surround it so Ias to act as a shield for it'. Thetwo terminals are insulated from each other, and the several parts andinsulating elements of the ordinary plugs must be carefully assembled inproducing the phone plugs now on the market.

Coaxial cables are used with telephone plugs to avoid seriousdisturbances in the telephone circuits from induetion currents caused bystray lields. The inner wire or core is surrounded by insulation and theother wire surrounds this insulation like a sleeve to serve as anelectrostatic shield for the inner wire. This sleeve is convenientlyformed by helically wrapping about the inner insulation a number of finewires `applied in side-by-side contact to form a band the side edges ofwhich touch in successive convolutions so that a continuous metal shieldis thus formed about the inner wire and its insulating coat. The end ofthis band of wires is connected directly or indirectly to the tubularterminal of the plug. As customarily done, this often leaves a gap inthe shield at the junction of the band and the tubular terminal. Toclose this gap, a metal sleeve of considerably larger diameter than thetubular terminal is usually provided to cover the gap Iand to serve alsoas a handle for manipulating the plug.

According to the present invention, the terminals of the plug aremanipulated in such a way as they are being assembled and soldered tothe cable that the formation of a gap in the shield is provided, and theinsulation between the terminals is introduced by injection so that theparts of the plug are more easily and compactly assembled, the heavymetal handle is eliminated, and the number of parts of the plug ismaterially reduced.

For a more complete understanding of the invention, reference may be hadto the following description thereof, and to the drawing, of which-Figure l is a perspective view of a telephone plug embodying theinvention;

Figure 2 is an elevational view, on a larger scale, of the two-wirecoaxial cable to be attached to the plug, parts being broken away toshow the various elements of the cable in sections;

Figure 3 is an elevational view of the cable shown in Figure 2, with atubular plug terminal in position to be attached to the outer wire, theterminal being partly broken away;

Figure 4 is an elevation of the cable with both terminal members of theplug attached thereto, the tubular terminal being shown in sections;

Figure 5 is an elevation of the cable with a sectional view of thecompleted plug thereon; and

Figure 6 is a section on the line 6 6 of Figure 5.y A conventionaltelephone plug consists pri-marily of two terminals connectedrespectively to the wires of a 2-wire I cable.y The two terminals are,respectively, a ball tip and' i' a cylindrical tubular sheath, the outerdiameter of both sulated' therefrom. For convenience of manufactureandhandling, the tubular outer conductor may be in the form of a band orribbon of smalll wires arranged in side-byside contact. These wires arewound helically around the insulation which surrounds the central orinner conductor. Since the successive convolutions of the helix are inedge to edge contact, the result is a continuous sleeve which actseffectively as a shield for the inner conductor against induction fromstray fields.

According to the presentl invention, as illustrated on the drawing, theplugcomprisesa ball tip 10 ofA standard size and shape and a sheath 12,which is of standard diameter and is preferably ll/s long. These partsare of metal, preferably nickel-plated brass. The improved plug can bestbe described by the methods by which it is attached to the two-wirecable 16. This cable consists of a central conductor 18, which ispreferably a stranded wire and is surrounded by a covering of suitableexible insulation material 2t). Helically wound on the insulation 20 isa band of wires arranged Side by side so that they constitute an outerconductor 22 which is virtually tubular and thus shields the inner orcentral conductor 18. The outer conductor 22 is covered by a protectiveand insulating coating 24.

The ball tip 10 consists of a knob-like extremity with a diameter of 1A"and a neck 26 of reduced diameter which widens out to a base 28 havingthe' same diameter as the ball. From the center of this base a hollowstem 30 projects, having a length of 5/16, an outside diameter of aboutj7/10", and a small axial bore. The sheath 12 is a metal tube having anouter diameter of 1A and a length of 1% In preparing the cable 16 forconnection to the terminal members 10 and 12, the outer layer ofinsulation 24 is stripped from the end portion of the cable to expose alength Vof the outer conductor 22 which is at least half the length ofthe sheath 12 and preferably is slightly longer than the sheath, e. g.,11./4. The next step is to unwind part or all of the exposed outerconductor, but for a distance from the end of the cable less than thelength of the sheath 12. If, for example, 1% of the conductor 22 hasbeen exposed, about is unwound, the remaining 1/2 being seized bysuitable means such as a bit of adhesive tape 34. The inner insulationis then stripped to expose about 3716 of the central conductor. Theunwound portion of the wire 22 is twisted into a single strand asindicated in Figures l, 2, 3 of the drawing and this strand is bent backfrom the end of the cable. The sheath 12 is then slipped over the end ofthe cable until the exposed portion of the central conductor 18 emergesfrom the trailing end 36 of the sheath 12. The hollow stem 30 of theball tip is sweated to the stripped portion of the central conductor 18so as to make a soldered joint therewith. The sheath 12 is thenretracted until its trailing end 36 is spaced about 1/16 from the base28 of the ball tip. As is evident from the drawing, the tubular shieldformed by the outer conductor 22 of the cable extends unbroken into theleading end of the sheath 12 and the clearance between the outerconductor and the sheath is small, so thatthere is no gap in theshielding of the inner conductor 18. No additional shielding membertherefore is required. Y

The twisted strand of wires of the conductor 22 is then bent around theleading end of the sheath 12 and is soldered as at 38 to the sheath, asindicated in Figure 4. The parts thus assembled are then placed in asuitable jig (not shown) by which the sheath 12 and ball tip 10 are heldin spaced aligned position. The jig is preferably part of a mold intowhich liqueed plastic material is injected by a suitable means (notshown). This plastic fills the space between the interior of the sheath12 and the cable parts and stem 30 therein and also lls the narrow gapbetweenthe trailing end 36 of the sheath 12 and the base 28 of the balltip 10. The mold in which the plastic is injected may be, and preferablyis, made to form in addition a cylindrical block 44 which envelops thesoldered joint 38, the leading end portion of the sheath 12, and theadjacent portion of the cable 16. This block 40 gives the plug a nishedappearance, it is light in weight, and it also serves as a convenienthandle by which the plug can be manipulated.

I claim:

A telephone plug having as terminals a tubular metal sheath and a balltip having a diameter greater than the interior diameter of said sheath,in combination with a coaxial cable comprising a central conductor,insulation surrounding said conductor, and an outer conductorsurrounding said insulation; said cable extending into one end of saidsheath, said central conductor being electrically connected to said balltip at the other end of said sheath, said outer conductor extendingunbroken into said sheath and having a direct soldered connection withsaid sheath, the clearance between said outer conductor and said sheathbeing small, whereby said central conductor is completely shielded bysaid sheath and the outer conductor, and a unitary body of moldedplastic insulation filling the remaining space in said sheath,insulating said ball tip from said sheath and covering the solderedjoint between said outer conductor and sheath, the end portion of thesheath remote from the ball tip, and a portion of said cable outside ofand adjacent to said sheath.

References Cited in the le of this patent UNITED STATES PATENTS OTHERREFERENCES `Electrical Manufacturing, December 12S-130.

1952, pages

